Thermionic tube



Aug. 6, 1935. D. K. LIPPINCOTT ET-AL- THERMIONIC TUBE Fil ed July 29, 1932 1 INVENTORS,

00mm K. L/PP/NCOTT &

HE/?BERT E. Mama/ BY W4 ATTORNEY Patented Aug. 6, 1935 UNITED STA S 'THEBMIONIC TUBE Donald K. Lippincott, Larkspur, and Herbert E. MetcaIf, Walnut Creek, Califl, .assig'nors to Heintz & Kaufman,.Ltd., San Francisco, Calif., acorporation of Nevada A -I tros, 1952, Serial No. 626,157

a Claims. (cram-27.5)

Our invention relates to a thermionic tube having a high mutual conductance and. more particularly to such a tube havinga cathode interposed between an anode and control electrode,

5 and a positively charged auxiliary electrode located inthe plane of the filament. The tube is adapted tobeusedxas an oscillator and amplifier at high frequencies-tor the transmission of radio information, and when so used-has a high power output. 1 7

Some of the objects'ofour invention are: To provide a thermionic tubehaving a high mutual conductance and consequent high power output; to provide a means for raising the-amplification factor of a thermionic tube having a cathode interposed between an anode and'a control electrode; to prov'ide aposit'ively charged auxiliary electrode in the plane of the cathodeto raise the mutual conductance of a thermionic tube having a cathode interposed between an anode and a control electrode; and to provide a thermionic oscillator and amplifier tube ofsimple construction and high poweroutput. Other objects of our invention will be apparent or will be specifically pointed out in the descriptionforming a part of this specification, but we do not limi-tourselyes to the embodiment of our invention herein described, as various forms may be adopted within the scope of theclaim's.

In the accompanying drawing forming a part of this specification, illustrating-a preferred embodiment of our invention,

Figure 1 shows an exterior view of the-invention. i

Figure 2 is a longitudinal sectionalwiewshowing the positioning of the-elements of thetube.

Figure 3 is a cross sectional view taken in the planeindicated by the line 3-- 3 in Figure 2'. a

' Figure 4 is'a schematic diagram-reduced'to-its lowestterms, showing a circuit in'which the tube maybe used. g

V Thermionic tubeshaving a cathode interposed between a control electrode and an anode are very satisfactory converters at high frequencies, *due to thefact that the cathode acts as a grounded shield between the two electrodes and the control electrode-anode capacity is thereby greatly reduced. If an attempt is made to carry this effect too far, however, the cathode shielding greatly reduces the amplification constant of the tube.

Our invention comprises, in its broadest terms, a, thermionic tube having a cathode located between a control electrode and an anode, and an auxiliary electrode in the plane of the filament energized at a potential less positive than "the anode. The emission from thecathode is thereby brought under greater control, and the amplifioation constant and mutual conductance is raised. a l i In the several figures, showing a specific form of the invention, a bulb l of heat-resistant glass, is' provided with control electrode stems 2 and anode stems 3. Anode support leads 5 are passed through the end of the stem at an anode seal 6 forming an air-tight joint.

The anode support 5 is inserted into a yoke 1 locked on securely by a nut 8. An anode body 9 is provided with a stiffening rib Ill securely welded to its major plane surface and the outturned flanges H of this rib slidably cooperate with arms I 2 of the yoke. A pin Mpasses through both the arms and the flanges, is secured by the lock-nut I5, and the anode body is thus firmly supported.

1 While not shown in the-drawing there are two of them support assemblies, one for each stem, located near the upper and lower borders of the anode. l a

The anode is made rigid on the edges by stiifeningflan'ges l5. 'The'material of the complete assembly may be of some refractory metal easily degassed-in vacuo, such as tantalum or tungsten.

The control electrode I! is identical in size,

shape and support, with the anode, being held securely'in place by the support l9, yoke 20, rib 2i, and pin .22. Flanges Mrstiffen the edges. The own end of the bulb is provided with a reentrant stem having cathode leads 25' sealed through a press 26 which also supports the dummy wires .21 and 28 on the outside of the cathode leads, :and the two ends 29 andi3il of a hairpin shaped wire 3 I. extend above the top of the anode and control electrodes andareinserted into a filament support bridge 32 of isolantite or lava, a good insulatnr-under vacuum and heat conditions. Holes 34 and 35 are bored in the bridge, a compoundfilamenthookflfi inserted, and springs 31 and 38 are slipped over "the hook ends and fastened by the welds and MI.

A filamentary cathode H is fastened to the cathode leads by welds 42 and 44, looped over the bends 45 and 46 in the compound hook, being maintained in position by the tension of the springs. The top portion 4'! of the hairpin is arranged to clear the cross portion 48 of the filament, and the straight portions of the filament are adjusted to be parallel and in the plane of the up- The two dummy wires 2'! and 28 right portions of the wires 21, 28, and 3|. The cathode and the coplanar wires are offset toward the control electrode so that they are closely adjacent the control electrode.

Near the point where the wires emerge from the press, electrical conducting jumpers 48 and 49 connect wires 27 and 28 with the hairpin 3i. Jumper 49 is extended downwardly by a bend 59 and connected to a lead 5| by a flexible connection 52. The lead 5! is sealed through the envelope in the usual manner.

It will be noted that the wires 21, 28, and the hairpin 3! are all electrically connected, and together constitute an auxiliary electrode lying in the plane of the cathode which may be energized through the lead 5|.

After all assembly and adjustment has been made as described, the complete tube is evacuated and sealed in the usual manner. Connection caps 52 are applied to the anode and control electrode stems 2 and 3, held in place by cement 54, and electricallyconnected to the support leads by a weld 55 as shown in Figure 3. A base may be used around the lower part of the tube if desired.

One circuit in which the invention may be utilized is shown diagrammatically and reduced to its lowest terms in Figure 4. Here, the complete auxiliary electrode is designated by the numeral 56. a

An input circuit, represented by lines 5'! and 58, is connected to the control electrode IT and the cathode 4 I. The anode, or output circuit starts at the cathode, passes through a source of potential 59, the positive end of which is connected to the anode 9 through the primary 5% of an output transformer 6 It is customary to shunt this primary, particularly in radio frequency circuits, by a condenser 62. The auxiliary electrode 55 is connected to the potential source 59 at a point 64 less positive than the anode, and is connected to the cathode through a grounding capacity ,65, which places the auxiliary electrode at the same radio frequency potential as the cathode, while the connection to the potential source provides a steady positive bias.

The path of the electrons in a tube having a cathode only, interposed between anode and control electrode, is largely at right angles to the control electrode, and the emitting wires of the oathode shield a large number of electrons from the action of the control electrode, being directly interposed. However there is a small normal divergence of the stream as it passes to the anode, due to the mutual repulsion of the negative charges, so that the electrostatic field of the control electrode passes between the cathode wires and affects a certain portion of the emission.

There is, however, a substantial part of the emission which the control field cannot reach, and which passes directly to the plate. A low amplification constant results.

When a positive potential is placed on the auxiliary electrode in the tube of our invention, the electron path is widened, as shown diagrammatically in Figure 3, and the electrons are brought into the space between the filament Wires. Here the control electrode may act on them, and a relatively small number of them reach the plate without being controllable.

Changing the angular path thus results in greatly increased control, an increased amplification constant, and a higher mutual conductance.

As the auxiliary electrode is grounded through the condenser 65, the combination of the filament and auxiliary electrode is an effective R. F. shield.

The combined actions results in a tube having a low control electrode-anode capacity, combined with a high mutual conductance and consequent power output, especially at high frequencies.

We claim:

1. A thermionic tube consisting of an envelope, a pair of electrically separate, opposed, planar and parallel electrodes mounted therein, a plurality of parallel rods occupying a plane intermediate the planes of said electrodes and parallel thereto, said rods being spaced to provide an aperture extending across one dimension of said plane, and a filamentary cathode positioned in said aperture, in the same plane as said rods and parallel therewith.

2. A thermionic tube consisting of an envelope, a pair of electrically separate, opposed, planar and parallel electrodes mounted therein, a plurality of parallel rods occupying a plane intermediate the planes of said electrodes and parallel thereto, said rods being spaced to provide an aperture extending across one dimension of said plane, a filamentary cathode positioned in said aperture, in the same plane as said rods and parallel therewith, and means for making electrical connection from outside said envelope to all of said rods.

3. A thermionic tube consisting of an envelope, a pair of electrically separate, opposed, planar and parallel electrodes mounted therein, a plurality of parallel rods occupying a plane intermediate the planes of said electrodes and parallel thereto, said rods being spaced to provide an aperture extending across one dimension of said plane, a. filamentary cathode positioned in said aperture, in the same plane as said rods and parallel therewith, an insulating bar supported by certain of said bars, and resilient means mounted onsaid bar for tensioning said cathode.

4. A thermionic tube consisting of an envelope, a pair of electrically separate, opposed, planar and parallel, electrodes mounted therein, a grid having apertures therein occupying a plane intermediate and parallel to the planes of said electrodes, said apertures extending substantially across one dimension of said electrodes, and a filamentary cathode disposed in said apertures in the plane of said grid.

5. A thermionic tube consisting of an envelope, a pair of electrically separate, opposed, planar and parallel electrodes therebetween, and a plurality of spaced parallel conductors occupying a plane intermediate the planes of said electrodes and parallel thereto, alternate conductors only being electron emitting, said conductors being free from physical and electrical contact during the major portion of their extent between said electrodes.

DONALD K. LIPPINCOTT. HERBERT E. METCALF. 

